Multi-factor authentication is an authentication method that requires the entity seeking to be the authenticated (e.g., a computer system user) to present two or more of the three basic authentication factors: the knowledge factor (“something only the user knows”), the possession factor (“something only the user has”), and the inherence factor (“something only the user is”). The more factors are employed by the authentication process, the higher is the probability that the user indeed possesses the asserted identity. Two-factor authentication is commonly employed in computer authentication, where the user may be required to supply a set of credentials covering the knowledge factor and the possession factor (e.g., a user password and a one-time code), or the knowledge factor and the inherence factor (e.g., a user password and a biometric input).
While multi-factor authentication is commonly regarded as strong authentication, other strong authentication varieties are known. In other words, strong authentication does not have to be multi-factor authentication. In an illustrative example, soliciting answers to multiple challenge questions may be regarded as a strong authentication method, but not multi-factor authentication, since multiple knowledge factors are provided. In another illustrative example, an authentication method which does not involve transmitting the password provides strong authentication.